This invention relates to a metering valve, particularly a fuel injection valve for an internal combustion engine and is of the type which has a valve needle slidably supported in a valve housing and arranged to open or close at least one metering aperture (nozzle opening) communicating with a supply line in which the pressurized medium to be metered is advanced. The valve needle is actuated to move into its open position by an actuating member formed of a component which, under the effect of a field varies its dimension at least in one direction. The valve needle is returned into its closed position by spring force.
The above-outlined metering valve, apart from its use to inject fuel in a pulsating manner, may be used to meter other fluids such as liquids or gases including vapors.
In the direct injection of diesel fuel or gasoline into the work chambers of internal combustion engines, particularly those used for driving automotive vehicles - which is the preferred mode of application of the invention - the high-pressure injection has distinct advantages as compared to the conventional low-pressure injection into an intake (suction) pipe. These advantages manifest themselves particularly in the avoidance of hot-starting problems. In high-pressure injection the fuel is continuously available at correspondingly high pressure and the valve needle for opening the metering aperture (injection nozzle) is operated by introducing external energy. To achieve sharp actuating pulses of defined duration, piezoelectric devices or actuating assemblies operating according to the principle of magnetostriction have been used. These assemblies thus involve actuating members which vary their dimensions under the effect of an electric or magnetic field.
Thus, European Patent 218,895 describes a metering valve of the above-outlined type, used as a fuel injection valve, which in an axial sequence has a piezoelectric stack actuator, a guided force-transmitting pin and a valve needle. The valve needle terminates in a valve head which externally extends over the metering aperture (injection nozzle opening) for closing the same. The piezoelectric stack actuator is disposed in a housing chamber which is connected with a fuel supply and which constitutes a storage chamber for the fuel. For returning the valve needle into the closed position from the position in which it maintains the injection nozzle open, a coil spring is used which surrounds the valve needle and is compressed between a flange forming part of the valve needle and a countersupport forming part of the valve housing.
The accommodation of the actuating member in a fuel-filled chamber involves problems particularly in case the fuel contains water since, for example, in a piezoelectric actuating member voltages in the order of magnitude of 150 volts and higher may be present.